0.2.2 Alpha Release 2

Added

The QPicamera2 widget will now display YUV420 images if the cv2 (OpenCV) module is installed.
Methods that allow still captures to be saved to files have been updated to accept file-like objects, such as BytesIO.
NOGUI=1 environmental variable to install without GUI dependencies
The Picamera2's request_callback has been changed to post_callback. A new pre_callback has been added which runs before images copied for applications.
Support for multiple outputs for the encoder

Changed

The still_configuration defaults now specify the default display and encode streams as none. The resolutions are often so large that the images can be problematic and there are often better alternatives (e.g. specifying a lores stream and displaying that instead).
The preview window implementations are changed to preserve image aspect ratios which they did not previously. The Qt variants also respect resize events.

0.2.1 Alpha Release

https://pypi.org/project/picamera2/0.2.1/

Added

Everything installable via apt and pip.
Many new examples.

Changed

Revised API - please refer to README.md file and examples.

In detail

Update README to clone using https and not SSH by @6by9 in #1
Add a TensorFlow Example by @aallan in #3
Update drm_preview.py by @tvoverbeek in #9
Tidy Up Logging by @meawoppl in #12
Added context manager. by @IanTBlack in #23
Add an encoder class that allows multi-threaded software encode by @davidplowman in #26
Fix typo by @davidplowman in #47
Rename default_controls to camera_controls by @davidplowman in #42
Add some more of the existing examples to the test suite by @davidplowman in #41
Qtgl fix by @davidplowman in #45
Include EXIF data when saving JPEG files by @davidplowman in #50
Improve style checker to spot and complain about merge commits by @davidplowman in #55
Add tuning parameter to Picamera2 constructor by @davidplowman in #52
Overlays by @davidplowman in #49
Add "#!/usr/bin/python" to the top of overlay examples by @davidplowman in #59
Add offset and window frame controls to preview windows by @davidplowman in #61
Fix leak of OpenGL texture handles by @davidplowman in #68
Some previews hang on to the last request; they must release it when … by @davidplowman in #73
Change the default logging level by @davidplowman in #75
Make the Qt signal/slot mechanism easier to use by @davidplowman in #72
Initial setup.py by @chrisruk in #53
Circular buffer by @chrisruk in #54
Fix an OpenGL check for versions of GLES earlier than 3.0 by @davidplowman in #78
Documentation: update installation instructions by @davidplowman in #77
Import cleanup by @meawoppl in #82
Async Cleanup by @meawoppl in #83
Update contributing guidelines to be a bit clearer by @davidplowman in #89
Display encode improvements by @davidplowman in #79
Preemptive check if camera_manager.cameras is empty by @Luraminaki in #91
Dng support by @davidplowman in #93
Initial attempt to set gop size by @chrisruk in #92
Optimise memory for still capture by @davidplowman in #80
Use enums for camera controls by @davidplowman in #85
Make Picamera2.start() create the event loop automatically by @davidplowman in #74
Preview merge by @davidplowman in #90
PyPI packaging by @grega in #100
Add V4L2 MJPEG encoder and example by @chrisruk in #101
Fix broken import for MJPEG server by @chrisruk in #103
Simplifying imports by @chrisruk in #105
Include outputs directory in setup.py by @chrisruk in #106
Improve yuv_to_rgb.py example by @davidplowman in #107
New FfmpegOutput class allows writing of mp4 files and audio streams by @davidplowman in #104
Add setup.py requirement for ffmpeg output by @chrisruk in #108
Fix small syntax warning by @davidplowman in #109
Fix some Qt complaints caused by the location of various imports by @davidplowman in #110
An extra recording example by @davidplowman in #112
Integration with the upstream libcamera tree. by @naushir in #113
Remove controls parameter from start method by @davidplowman in #115
Update documentation and setup.py for alpha release by @davidplowman in #117